The goal of this research is to develop a new method of intravascular imaging, which has the possibility of identifying atherosclerotic lesions. The lesions would then be characterized as to their potential for progression to alteration or rupture. The possibility of identifying and discriminating those lesions which are at risk for rupture has great significance. The applicants proposed to use optical coherence tomography (OCT) to develop a high resolution intravascular imaging system for the diagnosis of atherosclerotic lesions. The applicants noted the analogy of OCT to B Mode ultrasound imaging. However, the use of infrared light rather than acoustical waves should provide high resolution, broad dynamic range, and easy integration into cardiovascular catheter systems. The principal focus of this application is the development of background feasibility experiments designed to assess the feasibility of this approach. These background experiments focus on identifying advantages and limitations of OCT for intravascular imaging and maximizing performance. The specific aims are: 1) To perform imaging on a wide range of plaque morphologies and vascular components; 2) To determine the limitations associated with imaging through whole blood; 3) To identify the optimal incident wavelength for OCT imaging of the vasculature; 4) To directly compare the ability of both OCT and high frequency ultrasound (IVUS) to assess micropathology within human atherosclerotic plague in virtu; and 5) To demonstrate the ability of OCT and IVUS to perform in vivo imaging of an intravascular stent within a rabbit aorta.